Electronic circuit



Nov. 9, 1965 VOLTAGE AND CURRENT IGNITION COIL PRIMARY CURRENT T. A. BYLES 3,216,408

ELECTRONIC CIRCUIT Filed Feb. 13, 1964 TO DISTRIBUTOR FIG. 1

r I F 2 PRIMARY CURRENT II 4| 43 COLLECTOR CURRENT 42 INDUCED VOLTAGE IN SECONDARY TIME FIG. 3

46 N0 BALLAST ffl BALLAST I20 M.PH./ I 60 TIME KILOVOLTS I5 NO BALLAST BYPASS ENGINE R.P.M.

INVENTOR Y Theodore A. ByIes United States Patent 3,216,408 ELECTRONIC CIRCUIT Theodore A. Byles, Villa Park, 111., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed Feb. 13, 1964, Ser. No. 344,572 7 Claims. '(Cl. 123-148) This invention relates to ignition systems for internal combustion engines, and more particularly to an ignition system having improved high speed performance.

Many ignition systems for internal combustion engines use an intermittent switch to interrupt current in an ignition coil to develop high voltage firing pulses for the engine. The intermittent switch may be mechanical breaker points, or a transistor or similar semiconductor switch. Because the voltage supply for the ignition coil, usually a storage battery, may be lower during starting than during normal operation, the ignition coil may be designed for operation at this lower voltage, and a ballast resistor switched in series with the coil after the starting operation is completed.

In an ignition system of the above described nature, a decline in the voltage of the firing pulses may occur at high engine speeds. The mechanical breaker points or semiconductor switch are synchronized with the engine and are closed for a period of time which is inversely proportional to the engine speed. Each time the points or switch open, the field in the primary of the ignition coil collapses, producing the high voltage pulse in the secondary. When the points or switch close, it takes a certain amount of time for the primary current to build up to a level where cut-off will produce a satisfactory high voltage pulse. At medium or low speeds, the duration of point or switch closure is longer than the time it takes the primary current to reach its maximum level. At high speeds, however, the period during which the points or switch are closed becomes sufiiciently short that the current in the primary winding of the ignition coil at the instant of opening will not have had time to reach a proper level. This results in a marked reduction in the voltage of the firing pulses induced in the secondary winding.

Accordingly, it is an object of this invention to provide an ignition system for an internal combustion engine which has improved high speed operations.

Another object of the invention is to provide an economical way of modifying an existing ignition system to obtain improved high speed performance.

A feature of the invention is the provision, in an ignition system for an internal combustion engine, of a semiconductor switch in parallel with the ballast resistor, and a bias circuit for closing the switch to bypass the ballast resistor for a predetermined period during the initial part of the charging period for the ignition coil.

Another feature of the invention is the provision of means for bypassing the ballast resistor in an ignition system for an internal combustion engine, which means include a semiconductor switch for connection in parallel with the ballast resistor and a bias circuit for closing the switch to bypass the ballast resistor for a predetermined time during the initial part of each charging period for the ignition coil.

Referring now to the drawings:

FIG. 1 is a schematic diagram of a circuit constructed in accordance with the invention;

FIG. 2 contains plots of the primary current and the induced voltage in the secondary of the triggering transformer of FIG. 1, and the collector current for the transistor of FIG. 1, all with respect to time;

FIG. 3 contains plots of the ignition coil primary current when the transistor of FIG. 1 is conducting and when the transistor is cut off, both with respect to time; and,

FIG. 4 contains a plot of the voltage developed in the secondary of the ignition coil of FIG. 1 with respect to the speed of the engine.

The ignition system of the invention includes a ballast resistor, an ignition coil for supplying high voltage firing pulses to the internal combustion engine, and an intermittent switch for supplying current to the ignition coil and then cutting off the current to cause collapse of the field in the ignition coil for producing the high voltage pulse. The intermittent switch may be mechanical breaker points or one or more transistors or similar semiconductor switches, either the points or transistor being operable in timed relation with the internal combustion engine.

Means are provided for intermittently bypassing the ballast resistor to conduct increased current to the ignition coil during a portion of the period during which current is flowing in the coil. Such means comprise a semiconductor switch, such as a transistor, connected in parallel with the ballast resistor. A bias circuit is connected to the switch for closing the same for a predetermined time during the initial part of the period during which current is flowing in the coil. The bias circuit may include a transformer having a primary winding connected across the source of potential and a secondary winding connected across the emitter and base portions of the transistor.

Referring now to FIG. 1 the ignition system of the invention is depicted schematically. A storage battery 11 supplies voltage to the system and is charged by a generator 12 having a regulator 13 associated therewith. Generator 12 could be an alternator with associated rectifiers. Battery 11 is connected through an ignition switch 14 and a ballast resistor 15 to the primary winding 16 of an ignition coil 17. Primary winding 16 is inductively coupled to a secondary winding 18 and both windings are grounded through a pair of intermittently opening breaker points 19. A condenser 20 is connected across the points to reduce sparking therebetween.

As is well known in the art, points 19 are operable in synchronism with the internal engine to cause an intermittent flow of current through primary winding 16. As the current therethrough is interrupted due to the opening of the points 19, the collapse of the field in the primary winding 16 induces an extremely high voltage spike in secondary winding 18 which is then applied to the moving contact of the distributor (not shown), and from there to the spark plugs of the internal combustion engine for firing the fuel mixture in the cylinders.

Ignition coil 17 is designed for optimum operation at a particular voltage and current which is generally lower than the normal operating voltage and current provided by the battery. Accordingly, ballast resistor 15 is interposed between the coil and the battery to drop the voltage and limit the current. A starter motor 21 is connected across battery 11 through starter switch 22. During starting the drain on battery 11 is such as to lower its terminal voltage, and to compensate for this lower voltage a switch 23 is ganged with switch 22 to bypass ballast resistor 15 during starting. This enables the coil 17 to operate close to the voltage and current for which it was designed, during starting as well as during normal running conditions.

The foregoing description has thus far been that of a type of ignition system which is well known in the art. Numerous variations of the basic idea of the foregoing described ignition system are of course, prevalent in the art. For example, breaker points 19 might be replaced by a semiconductor switch, such as a transistor, operable by a bias circuit associated therewith to switch on and off in timed relation with the internal combustion engine. The addition of various accessories might also be desired in such a system, as might the variation in the location of the components, such as for example, placing the breaker points or semiconductor switch between the voltage source and the ignition coil, or utilizing a negative ground system rather than a positive ground system as shown.

A disadvantage common to many ignition systems of the foregoing described type is that at high engine speeds, for example when a typical passenger car engine is driving the car at about 60 miles per hour or more, the voltage spike produced in the secondary winding of the ignition coil may fall off to a low level with a consequent reduction in efficiency. Where a ballast resistor is utilized in the system, the invention contemplates providing means for bypassing this ballast resistor at critical times during each pulse in order to prevent a fall off in the voltage of the firing pulses. In accordance with the invention, a transistor 31 has its emitter and collector electrodes, 32 and 33 respectively, connected across the ballast resistor 15. A trigger transformer 34 provides bias for transistor 33 for switching the transistor on and off. Transformer 34 includes a primary winding 35 connected between the voltage source and the points, and a secondary winding 36 connected across the emitter electrode 32 and the base electrode 37 of transistor 33.

At the instant points 19 close and current begins to flow in primary winding 16 of ignition coil 17, a gradual build up of current will occur in primary winding 35 of transformer 34, shown by curve 41 in FIG. 2. The initial build up of current in primary winding 35 will induce a voltage in secondary winding 36 as shown by curve 42. This voltage will rise rapidly to a peak and then decline almost as rapidly to zero when the current in primary winding 35 has built up to a constant value. The collector current of transistor 31 will follow generally curve 42 and is indicated by curve 43 of FIG. 2. It may be seen therefore, that as a consequence of biasing transistor 31 by means of transformer 34, the ballast resistor 15 is bypassed for a short time at the beginning of each period during which current flows in primary winding 16 of ignition coil 17. Components should be selected to result in a bypass time of approximately 3 to milliseconds.

Referring now to FIG. 3, the reason for the fall off of the high voltage pulses at high speeds may be more clearly understood. According to well known laws, it will take a certain length of time during each period of closure of the intermittent switch for current through primary winding 16 of ignition coil 17 to build up sufficiently so that the voltage induced in secondary winding 18, upon collapse'of the field in ignition coil 17, will provide the desired high voltage pulse for ignition. With ballast resistor in the system, the rising current in primary winding 16 is represented by curve 45 of FIG. 3. At slower and moderate engine speeds, the period of time during which points 19 are closed is long enough to permit the current in primary winding 16 to build up to a suflicient level. At higher speeds, however, breaker points 19 open rapidly, after about 2 to 4 milliseconds, so that the current may not have time to build up to suflicient levels. With ballast resistor 15 shorted out, the current in primary winding 16 would rise as shown in curve 46 of FIG. 3, that is, much more rapidly. If ballast resistor 15 were left shorted, however, the current would rise to a high value such that the danger of damage to the ignition coil would be increased. By providing transistor 31 and transformer 34 in the ignition circuit as described, so that the operation of the circuit is as shown in FIG. 2, transistor 31 will conduct to bypass ballast resistor 15 to permit current in primary winding 16 to build up initially along curve 46 rather than curve 45. After the transformer 34 is finished pulsing, the current in primary winding 16 of ignition coil 17 will follow curve 47 and stay on the level of curve 45 for safe operation of ignition coil 17. Component values should be selected to achieve a smooth transition.

Referring to FIG. 4, the results of such a system are depicted in terms of the high voltage firing pulse supplied to the engine. Curve 51 represents the high voltage pulses in the ignition system shown in FIG. 1 if transistor 31 and transformer 34 were not present. Curve 52, on the other hand, shows how the high voltage pulses are increased, at increased engine speeds, when transistor 31 and transformer 34 are used as shown and described.

It may therefore, be seen that the invention provides an ignition system, for an internal combustion engine, which has improved high speed operation. In addition, many existing systems may be modified to attain improved high speed performance merely by the addition of transistor 31 and transformer 34 as shown and described.

I claim:

1. An ignition system for an internal combustion engine including in combination, a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, switch means operable in synchronism with the engine to be closed for a period of time which is inversely proportional to the speed of the engine conductor means for connecting said ballast resistor and said ignition coil and said switch means in series across a source of potential, and control means for intermittently bypassing said ballast resistor to conduct increased current to said ignition coil for a portion of the period during which said switch means is closed, said control means comprising a semiconductor switch connected in parallel with said ballast resistor, and further comprising bias means connected to said semiconductor switch for closing the same for a predetermined time during the initial part of the period during which said switch means is closed, said semiconductor switch when closed bypassing said ballast resistor to provide rapid build up of current in said ignition coil for improved high voltage at high speed.

2. An ignition system for an internal combustion engine including in combination, a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, switch means operable in synchronism with the engine to be closed for a period of time which is inversely proportional to the speed of the engine conductor means for connecting said ballast resistor and said ignition coil and said switch means in series across a source of potential, and control means for intermittently bypassing said ballast resistor to conduct increased current to said ignition coil for a portion of the period during which said switch means is closed, said control means comprising a transistor having base, emitter and collector electrodes with said emitter and collector electrodes thereof connected across said ballast resistor, said means further comprising bias means connected across said base and collector electrodes of said transistor for closing the same for a predetermined time during the initial part of the period during which said switch means are closed, said transistor when conducting bypassing said ballast resistor to provide rapid build up of current in said ignition coil for improved high voltage at high speeds.

3. An ignition system for an internal combustion engine including in combination, a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, switch means operable in synchronism with the engine to be closed for a period of time which is inversely proportional to the speed of the engine conductor means for connecting said ballast resistor and said ignition coil and said switch means in series across a source of potential, and control means for intermittently bypassing said ballast resistor to conduct increased current to said ignition coil for a portion of the period during which said switch means are closed, said control means comprising a transistor having base, emitter and collector electrodes with said collector and emitter electrodes thereof being connected across said ballast resistor, said means further comprising a trigger transformer having a primary winding connected in series with said switch means across the source of potential and having a secondary winding connected across said base and emitter electrodes of said transistor, said transistor when conducting bypassing said ballast resistor to provide rapid build up of current in said ignition coil for improved high voltage at high speed.

4. An ignition system for an internal combustion engine including in combination, a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, a pair of breaker points operable in synchronism with the engine, means for connecting said ignition coil and said ballast resistor and said breaker points in series across a source of potential, a transistor having base, emitter and collector electrodes with said emitter and collector electrodes connected across said ballast resistor, a trigger transformer having a primary winding connected across the source of potential in series with said breaker points and further having a secondary winding connected across said base and emitter electrodes of said transistor, said trigger transformer pulsing upon closure of said breaker points to cause said transistor to conduct and bypass said ballast resistor to conduct increased current to said ignition coil during an initial portion of the period during which said breaker points are closed to provide rapid build up of current in said ignition coil for improved high voltage at high speeds.

5. In an ignition system for an internal combustion engine having a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, an intermittent switch having a closed period inversely proportional to the speed of the engine, and conductor means connecting said ballast resistor and said ignition coil and said intermittent switch in series across a source of potential, control means for intermittently bypassing the ballast resistor to conduct increased current to the ignition coil during a portion of the closed period of the intermittent switch, said control means including in combination, a semiconductor switch adapted to be connected in parallel with the ballast resistor, and bias means connected to said semiconductor switch for closing the same for a predetermined time during the initial part of the closed period of the intermittent switch, during which predetermined time said semiconductor switch will bypass the ballast resistor to provide a rapid build up of current in the ignition coil for improved high voltage at high speed.

6. In an ignition system for an internal combustion engine having a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, an intermittent switch having a closed period inversely proportional to the speed of the engine, and conductor means connecting said ballast resistor and said ignition coil and said intermittent switch in series across a source of potential, control means for intermittently bypassing the ballast resistor to conduct increased current to the ignition coil during a portion of the closed period of the intermittent switch, said control means including in combination, a transistor having "base, emitter and collector electrodes, means for connecting said emitter and collector electrodes across the ballast resistor, and bias means connected across said base and emitter electrodes of said transistor for biasing said transistor into conduction for a predetermined time during the initial part of the closed period of the intermittent switch, during which predetermined time said transistor will bypass the ballast resistor to provide a rapid build-up of current in the ignition coil for improved high voltage at high speeds.

7. In an ignition system for an internal combustion engine having a ballast resistor, an ignition coil for supplying high voltage firing pulses to the engine, an intermittent switch having a closed period inversely proportional to the speed of the engine, and conductor means connecting said ballast resistor and said ignition coil and said intermittent switch in series across a source of potential, control means for intermittently bypassing the ballast resistor to conduct increased current to the ignition coil during a portion of the closed period of the source of potential, said control means including in combination, a transistor having base, emitter and collector electrodes, means for connecting said emitter and collector electrodes across the ballast resistor for bypassing the same upon conduction of said transistor, and bias means connected to said transistor for causing the same to conduct for a predetermined time during the initial part of the closed period of the source of potential, said bias means comprising a trigger transformer having a primary winding adapted for connection in series with the intermittent switch across the source of potential and further having a secondary winding connected across said base and said emitter electrodes of said transistor, during which predetermined time said transistor will bypass the ballast resistor to provide a rapid build up of current in the ignition coil for improved high voltage at high speeds.

No references cited.

RICHARD B. WILKINSON, Primary Examiner 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE INCLUDING IN COMBINATION, A BALLAST RESISTOR, AN IGNITION COIL FOR SUPPLYING HIGH VOLTAGE FIRING PULSES TO THE ENGINE, SWITCH MEANS OPERABLE IN SYNCHRONISM WITH THE ENGINE TO BE CLOSED FOR A PERIOD OF TIME WHICH IS INVERSELY PROPORTIONAL TO THE SPEED OF THE ENGINE CONDUCTOR MEANS FOR CONNECTING SAID BALLAST RESISTOR AND SAID IGNITION COIL AND SAID SWITCH MEANS IN SERIES ACROSS A SOURCE OF POTENTIAL, SAID CONTROL MEANS FOR INTERMITTENTLY BYPASSING SAID BALLAST RESISTOR TO CONDUCT INCREASED CURRENT TO SAID IGNITION COIL FOR A PORTION OF THE PERIOD DURING WHICH SAID SWITCH MEANS IS CLOSE, SAID CONTROL MEANS COMPRISING A SEMICONDUCTOR SWITCH CONNECTED IN PARALLEL WITH SAID BALLAST RESISTOR, AND FURTHER COMPRISING BIAS MEANS CONNECTED TO SAID SEMICONDUCTOR SWITCH FOR CLOSING THE SAME FOR A PREDETERMINED TIME DURING THE INITIAL PART OF THE PERIOD DURING WHICH SAID SWITCH MEANS IS CLOSED, SAID SEMICONDUCTOR SWITCH WHEN CLOSED BYPASSING SAID BALLAST RESISTOR TO PROVIDE RAPID BUILD UP OF CURRENT IN SAID IGNITION COIL FOR IMPROVED HIGH VOLTAGE AT HIGH SPEED. 